The old problem of which rook to move. Keymer probably considered it would be useful to give the king some space in case it needs to run from the attack, but the rook was useful on d1.
15... c4f7 An interesting move, vacating the c4-square for the knight. 16. d4e5 It's necessary to capture the knight before it goes to c4. 16... f6e5  17. f1e2  17... c7c5 Black starts a pawn advance on the queenside. White's position is very unpleasant.